Nonvolatile Charge Trap Memory Device Having A Deuterated Layer In A Multi-Layer Charge-Trapping Region

ABSTRACT

Scaling a charge trap memory device and the article made thereby. In one embodiment, the charge trap memory device includes a substrate having a source region, a drain region, and a channel region electrically connecting the source and drain. A tunnel dielectric layer is disposed above the substrate over the channel region, and a multi-layer charge-trapping region disposed on the tunnel dielectric layer. The multi-layer charge-trapping region includes a first deuterated layer disposed on the tunnel dielectric layer, a first nitride layer disposed on the first deuterated layer and a second nitride layer disposed

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S.application Ser. No. 11/904,475, filed Sep. 26, 2007, which claims thebenefit of priority under 35 U.S.C. 119(e) to U.S. Provisional PatentApplication Ser. No. 60/931,905, filed May 25, 2007, both of which areincorporated by reference herein.

TECHNICAL FIELD

The invention is in the field of Semiconductor Devices.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional wilts on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,lending to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

Non-volatile semiconductor memories typically use stacked floating gatetype field-effect-transistors. In such transistors, electrons areinjected into a floating gate of a memory cell to be programmed bybiasing a control gate and grounding a body region of a substrate onwhich the memory cell is formed. An oxide-nitride-oxide (ONO) stack isused as either a charge storing layer, as in asemiconductor-oxide-nitride-oxide semiconductor (SONOS) transistor, oras an isolation layer between the floating gate and control gate, as ina split gate flash transistor. FIG. 1 illustrates a cross-sectional viewof a conventional nonvolatile charge trap memory device.

Referring to FIG. 1, semiconductor device 100 includes a SONOS gatestack 104 including a conventional ONO portion 106 formed over a siliconsubstrate 102. Semiconductor device 100 further includes source anddrain regions 110 on either side of SONOS gate stack 104 to define achannel region 112. SONOS gate stack 104 includes a poly-silicon gatelayer 108 formed above and in contact with ONO portion 106. Polysilicongate layer 108 is electrically isolated from silicon substrate 102 byONO portion 106. ONO portion 106 typically includes a tunnel oxide layer106A, a nitride or oxynitride charge-trapping layer 106B, and a topoxide layer 106C overlying nitride or oxynitride layer 106B.

One problem with conventional SONOS transistors is the poor dataretention in the nitride or oxy-nitride layer 106B that limitssemiconductor device 100 lifetime and its use in several applicationsdue to leakage current through the layer. One attempt to address thisproblem focused on the use of silicon-rich SONOS layers, which enable alarge initial separation between program and erase voltages at thebeginning of life but result a rapid deterioration of charge storingability. Another attempt focused on oxygen-rich layers, which enable areduced rate of deterioration of charge storing ability, but also reducethe initial separation between program and erase voltages. The effect ofboth of these approaches on data retention over time may be showngraphically. FIGS. 2 and 3 are plots of Threshold Voltage (V) as afunction of Retention Time (Sec) for conventional nonvolatile chargetrap memory devices.

Referring to FIG. 2, rapid deterioration of charge storing ability for asilicon-rich layer is indicated by the convergence of the programmingthreshold voltage (VTP) 202 and erase threshold voltage (VTE) 204 to aspecified minimum 206. Referring to FIG. 3, a reduced separation betweenVTP 302 and VTE 304 is obtained for an oxygen-rich layer. As indicatedby line 306, the overall useful lifetime of device is not appreciablyextended by this approach.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not limitation, in the figures of the accompanying drawings inwhich:

FIG. 1 illustrates a cross-sectional view of a conventional nonvolatilecharge trap memory device.

FIG. 2 is a plot of Threshold Voltage (V) as a function of RetentionTime (Sec) for a conventional nonvolatile charge trap memory device.

FIG. 3 is a plot of Threshold Voltage (V) as a function of RetentionTime (Sec) for a conventional nonvolatile charge trap memory device.

FIG. 4 illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 5 illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 6A illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6B illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6C illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6D illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6E illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6F illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6G illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6H illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 6I illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 7A illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 7B illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 7C illustrates a cross-sectional view representing a step in theformation of a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention.

FIG. 8A illustrates a cross-sectional view of a nonvolatile charge trapmemory device including an ONNO stack.

FIG. 8B illustrates a cross-sectional view of a nonvolatile charge trapmemory device including an ONONO stack.

FIG. 9 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device includinga split multi-layer charge-trapping region.

FIG. 10A illustrates a non-planar multigate device including a splitcharge-trapping region.

FIG. 10B illustrates a cross-sectional view of the non-planar multigatedevice of FIG. 10A.

FIGS. 11A and 11B illustrate a non-planar multigate device including asplit charge-trapping region and a horizontal nanowire channel.

FIG. 11C illustrates a cross-sectional view of a vertical string ofnon-planar multigate devices of FIG. 11A.

FIGS. 12A and 12B illustrate a non-planar multigate device including asplit charge-trapping region and a vertical nanowire channel.

DETAILED DESCRIPTION

A nonvolatile charge trap memory device and a method to form the same isdescribed herein. In the following description, numerous specificdetails are set forth, such as specific dimensions, in order to providea thorough understanding of the present invention. It will be apparentto one skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownprocessing steps, such as patterning steps or wet chemical cleans, arenot described in detail in order to not unnecessarily obscure thepresent invention. Furthermore, it is to be understood that the variousembodiments shown in the Figures are illustrative representations andare not necessarily drawn to scale.

Disclosed herein is a nonvolatile charge trap memory device. The devicemay include a substrate having a channel region and a pair of source anddrain regions. A gate stack may be formed above the substrate over thechannel region and between the pair of source and drain regions. In oneembodiment, the gate stack includes a multi-layer charge-trapping regionhaving a first deuterated layer. The multi-layer charge-trapping regionmay further include a deuterium-free charge-trapping layer.Alternatively, the multi-layer charge-trapping region may include apartially deuterated charge-trapping layer having a deuteriumconcentration less than that of the first deuterated layer.

A nonvolatile charge trap memory device including a multi-layer chargetrapping region having a deuterated layer may exhibit improvedprogramming and erase speed and data retention. In accordance with anembodiment of the present invention, a deuterated layer is formedbetween the charge-trapping layer of the multi-layer charge trappingregion and the tunnel dielectric layer. In one embodiment, thedeuterated layer is essentially trap-free and mitigates hot electrondegradation during erase and program cycles. By incorporating atrap-free layer between the tunnel dielectric layer and thecharge-trapping layer of a multi-layer charge-trapping region, the Vtshift from erase and program cycles may be reduced and the retention maybe increased. In accordance with another embodiment of the presentinvention, a second deuterated layer is also formed between thecharge-trapping layer of the multi-layer charge-trapping region and atop dielectric layer of the gate stack.

A nonvolatile charge trap memory device may include a multi-layercharge-trapping region having a deuterated layer. FIG. 4 illustrates across-sectional view of a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

Referring to FIG. 4, semiconductor device 400 includes a gate stack 404formed over a substrate 402. Semiconductor device 400 further includessource and drain regions 410 in substrate 402 on either side of gatestack 404, defining a channel region 412 in substrate 402 underneathgate stack 404. Gate stack 404 includes a tunnel dielectric layer 404A,a multi-layer charge-trapping region 404B, a top dielectric layer 404Cand a gate layer 404D. Thus, gate layer 404D is electrically isolatedfrom substrate 402. Multi-layer charge-trapping region 404B includes adeuterated layer 406 between a charge-trapping layer 408 of multi-layercharge-trapping region 404B and tunnel dielectric layer 404A. A pair ofdielectric spacers 414 isolates the sidewalls of gate stack 404.

Semiconductor device 400 may be any nonvolatile charge trap memorydevice. In one embodiment, semiconductor device 400 is a Flash-typedevice wherein the charge-trapping layer is a conductor layer or asemiconductor layer. In accordance with another embodiment of thepresent invention, semiconductor device 400 is a SONOS-type devicewherein the charge-trapping layer is an insulator layer. By convention,SONOS stands for “Semiconductor-Oxide-Nitride-Oxide-Semiconductor,”where the first “Semiconductor” refers to the channel region material,the first “Oxide” refers to the tunnel dielectric layer, “Nitride”refers to the charge-trapping dielectric layer, the second “Oxide”refers to the top dielectric layer (also known as a blocking dielectriclayer) and the second “Semiconductor” refers to the gate layer. ASONOS-type device, however, is not limited to these specific materials,as described below.

Substrate 402 and, hence, channel region 412, may be composed of anymaterial suitable for semiconductor device fabrication. In oneembodiment, substrate 402 is a bulk substrate composed of a singlecrystal of a material which may include, but is not limited to, silicon,germanium, silicon-germanium or a III-V compound semiconductor material.In another embodiment, substrate 402 includes a bulk layer with a topepitaxial layer. In a specific embodiment, the bulk layer is composed ofa single crystal of a material which may include, but is not limited to,silicon, germanium, silicon-germanium, a III-V compound semiconductormaterial and quartz, while the top epitaxial layer is composed of asingle crystal layer which may include, but is not limited to, silicon,germanium, silicon-germanium and a III-V compound semiconductormaterial. In another embodiment, substrate 402 includes a top epitaxiallayer on a middle insulator layer which is above a lower bulk layer. Thetop epitaxial layer is composed of a single crystal layer which mayinclude, but is not limited to, silicon (i.e. to form asilicon-on-insulator (SOI) semiconductor substrate), germanium,silicon-germanium and a III-V compound semiconductor material. Theinsulator layer is composed of a material which may include, but is notlimited to, silicon dioxide, silicon nitride and silicon oxy-nitride.The lower bulk layer is composed of a single crystal which may include,but is not limited to, silicon, germanium, silicon-germanium, a III-Vcompound semiconductor material and quartz. Substrate 402 and, hence,channel region 412, may include dopant impurity atoms. In a specificembodiment, channel region 412 is doped P-type and, in an alternativeembodiment, channel region 412 is doped N-type.

Source and drain regions 410 in substrate 402 may be any regions havingopposite conductivity to channel region 412. For example, in accordancewith an embodiment of the present invention, source and drain regions410 are N-type doped regions while channel region 412 is a P-type dopedregion. In one embodiment˜substrate 402 and, hence, channel region 412,is composed of boron-doped single-crystal silicon having a boronconcentration in the range of 1×10¹⁵-1×10¹⁹ atoms/cm³. Source and drainregions 410 are composed of phosphorous- or arsenic-doped regions havinga concentration of N-type dopants in the range of 5×10¹⁶⁻-5×10¹⁹atoms/cm³. In a specific embodiment, source and drain regions 410 have adepth in substrate 402 in the range of 80-200 nanometers. In accordancewith an alternative embodiment of the present invention, source anddrain regions 410 are P-type doped regions while channel region 412 isan N-type doped region.

Tunnel dielectric layer 404A may be any material and have any thicknesssuitable to allow charge carriers to tunnel into the charge-trappinglayer under an applied gate bias while maintaining a suitable barrier toleakage when the device is unbiased. In one embodiment, tunneldielectric layer 404A is formed by a thermal oxidation process and iscomposed of silicon dioxide or silicon oxy-nitride, or a combinationthereof. In another embodiment, tunnel dielectric layer 404A is formedby chemical vapor deposition or atomic layer deposition and is composedof a dielectric layer which may include, but is not limited to, siliconnitride, hafnium oxide, zirconium oxide, hafnium silicate, hafniumoxy-nitride, hafnium zirconium oxide and lanthanum oxide. In a specificembodiment, tunnel dielectric layer 404A has a thickness in the range of1-10 nanometers. In a particular embodiment, tunnel dielectric layer404A has a thickness of approximately 2 nanometers.

Multi-layer charge-trapping region 404B may be composed of any materialand have any thickness suitable to store charge and, hence, raise thethreshold voltage of gate stack 404. In one embodiment, multi-layercharge-trapping region 404B is formed by a chemical vapor depositionprocess and is composed of a dielectric material which may include, butis not limited to, stoichiometric silicon nitride, silicon—rich siliconnitride and silicon oxy-nitride. In accordance with an embodiment of thepresent invention, multi-layer charge-trapping region 404B includes adeuterated layer 406 between tunnel dielectric layer 404A and chargetrapping layer 408, as depicted in FIG. 4. Deuterated layer 406 andcharge-trapping layer 408 may be composed of a deuterated derivative anda non-deuterated derivative, respectively, of the same material. Forexample, in accordance with an embodiment of the present invention,deuterated layer 406 is a deuterated derivative of silicon oxy-nitride,while charge-trapping layer 408 is formed from the hydrogenatedderivative of silicon oxy-nitride. In one embodiment, the totalthickness of multi-layer charge-trapping region 404B is in the range of5-10 nanometers. In a specific embodiment, the ratio of thicknesses ofdeuterated layer 406: charge-trapping layer 408 is approximately 1:1,respectively.

Multi-layer charge-trapping region 404B may have an abrupt interfacebetween deuterated layer 406 and charge-trapping layer 408. That is, inaccordance with an embodiment of the present invention, charge-trappinglayer 408 is deuterium-free. Alternatively, a gradient of deuterium atomconcentration moving from high concentration of deuterium in deuteratedlayer 406 ranging to low concentration of deuterium in charge-trappinglayer 408 may be formed. Thus, in accordance with an alternativeembodiment of the present invention, charge-trapping layer 408 is apartially deuterated layer, but having a deuterium concentration lessthan that of deuterated layer 406.

Top dielectric layer 404C may be any material and have any thicknesssuitable to maintain a barrier to charge leakage without significantlydecreasing the capacitance of gate stack 404. In one embodiment, topdielectric layer 404C is formed by a chemical vapor deposition processand is composed of silicon dioxide, silicon oxynitride, silicon nitride,or a combination thereof. In another embodiment, top dielectric layer404C is formed by atomic layer deposition and is composed of a high-kdielectric layer which may include, but is not limited to, hafniumoxide, zirconium oxide, hafnium silicate, hafnium oxy-nitride, hafniumzirconium oxide and lanthanum oxide. In a specific embodiment, topdielectric layer 404C has a thickness in the range of 1-20 nanometers.

Gate layer 404D may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of aSONOS-type transistor. In accordance with an embodiment of the presentinvention, gate layer 404D is formed by a chemical vapor depositionprocess and is composed of doped poly-crystalline silicon. In anotherembodiment, gate layer 404D is formed by physical vapor deposition andis composed of a metal-containing material which may include, but is notlimited to, metal nitrides, metal carbides, metal silicides, hafnium,zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum,cobalt and nickel.

A nonvolatile charge trap memory device may include a multi-layercharge-trapping region having more than one deuterated layer. FIG. 5illustrates a cross-sectional view of a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention.

Referring to FIG. 5, semiconductor device 500 includes a gate stack 504formed over a substrate 502. Semiconductor device 500 further includessource and drain regions 510 in substrate 502 on either side of gatestack 504, defining a channel region 512 in substrate 502 underneathgate stack 504. Gate stack 504 includes a tunnel dielectric layer 504A,a multi-layer charge-trapping region 5048, a top dielectric layer 504Cand a gate layer 504D. Thus, gate layer 504D is electrically isolatedfrom substrate 502. Multi-layer charge-trapping region 504B includes afirst deuterated layer 506 and a second deuterated layer 516 sandwichingcharge-trapping layer 508 of multi-layer charge trapping region 504 B. Apair of dielectric spacers 514 isolates the sidewalls of gate stack 504.

Semiconductor device 500 may be any semiconductor device described inassociation with semiconductor device 400 from FIG. 4. Substrate 502,source and drain regions 510 and channel region 512 may be composed ofany material and dopant impurity atoms described in association withsubstrate 402, source and drain regions 410 and channel region 412,respectively, from FIG. 4. Tunnel dielectric layer 504A, top dielectriclayer 504C and gate layer 504D may be composed of any material describedin association with tunnel dielectric layer 404A, top dielectric layer404C and gate layer 404D, respectively, from FIG. 4.

However, in contrast to semiconductor device 400, semiconductor deviceincludes a multi-layer charge-trapping region 5048 having seconddeuterated layer 516 above charge trapping layer 508, as depicted inFIG. 5. First deuterated layer 506 and charge-trapping layer 508 may becomposed of any material described in association with deuterated layer406 and charge-trapping layer 408, respectively, from FIG. 4.Additionally, second deuterated layer 516 may also be composed of anymaterial described in association with deuterated layer 406 from FIG. 4.However, in accordance with an embodiment of the present invention, thetotal thickness of multilayer charge-trapping region 504B is in therange of 5-10 nanometers, i.e. multi-layer charge-trapping region 504Bhas a thickness in the same range as multi-layer charge trapping region404B from FIG. 4. Thus, the relative ratios of thicknesses of deuteratedlayers and the charge-trapping layer may differ from those ofsemiconductor device 400. For example, in one embodiment, the ratio ofthicknesses of first deuterated layer 506:charge-trapping layer508:second deuterated layer 516 is approximately 1:2:1, respectively.

As with multi-layer charge-trapping region 404B from FIG. 4, multilayercharge-trapping region 504B may have an abrupt interface between firstdeuterated layer 506 and charge-trapping layer 508. Likewise, as secondabrupt interface may exist between second deuterated layer 516 andcharge-trapping layer 508. That is, in accordance with an embodiment ofthe present invention, charge-trapping layer 508 is deuterium-free.Alternatively, a gradient of deuterium atom concentration moving fromhigh concentration of deuterium in first and second deuterated layers506 and 516 ranging to low concentration of deuterium in charge-trappinglayer 508 may be formed. Thus, in accordance with an alternativeembodiment of the present invention, charge-trapping layer 508 is apartially deuterated layer, but having a deuterium concentration lessthan that of deuterated layers 506 and 516.

A nonvolatile charge trap memory device may be fabricated to include amulti-layer charge-trapping region having a deuterated layer. FIGS. 6A-Iillustrate cross-sectional views representing steps in the formation ofa nonvolatile charge trap memory device, in accordance with anembodiment of the present invention.

Referring to FIG. 6A, a substrate 602 is provided. Substrate 602 may becomposed of any material and have any characteristics described inassociation with substrates 402 and 502 from FIGS. 4 and 5,respectively.

Referring to FIG. 6B, a tunnel dielectric layer 620 is formed on the topsurface of substrate 602. Tunnel dielectric layer 620 may be formed fromany material, from any process, and have any thickness described inassociation with tunnel dielectric layers 404A and 504A from FIGS. 4 and5, respectively.

Referring to FIG. 6C, a multi-layer charge-trapping region 622 is formedon the top surface of tunnel dielectric layer 620. In accordance with anembodiment of the present invention, multi-layer charge-trapping region622 includes a deuterated layer 624 between tunnel dielectric layer 620and a charge-trapping layer 626, as depicted in FIG. 6C. Deuteratedlayer 624 and charge-trapping layer 626 may be composed of any materialsand have any thicknesses described in association with deuterated layer406 and charge-trapping layer 408, respectively, from FIG. 4.Multi-layer charge-trapping region 622 and, hence, deuterated layer 624and charge-trapping layer 626 may be formed by any process suitable toprovide substantially uniform coverage above tunnel dielectric layer620. In accordance with an embodiment of the present invention,multi-layer charge-trapping region 622 is formed by a chemical vapordeposition process. In one embodiment, deuterated layer 624 is formedfirst using deuterated formation gases and, subsequently,charge-trapping layer 626 is formed next using non-deuterated formationgases. In a specific embodiment, multi-layer charge-trapping region 622is composed substantially of silicon oxy-nitride, wherein deuteratedlayer 624 is first formed using formation gases such as, but not limitedto, deuterated silane (SiD₄), deuterated dichlorosilane (SiD₂Ch),nitrous oxide (N₂O), deuterated ammonia (ND₃) and oxygen (O₂).Charge-trapping layer 626 is then formed using formation gases such as,but not limited to, non-deuterated-bis(tert-butylamino) silane(non-deuterated-BTBAS), silane embodiment, deuterated layer 624 andcharge-trapping layer 626 are formed in the same process step, i.e.,they are formed in the same process chamber with a seamless transitionfrom deuterated formation gases to non-deuterated formation gases.

An abrupt deuterated and non-deuterated junction may be present at theinterface of deuterated layer 624 and charge-trapping layer 626. Thus,in accordance with an embodiment of the present invention,charge-trapping layer 626 remains deuterium free. Alternatively, some ofthe deuterium present in deuterated layer 624 may migrate tocharge-trapping layer 626 during the deposition of charge-trapping layer626 or during subsequent high temperature process steps. That is, agradient of deuterium atom concentration moving from high concentrationof deuterium in deuterated layer 624 ranging to low concentration ofdeuterium in charge-trapping layer 626 may be formed. Thus, inaccordance with an alternative embodiment of the present invention,charge trapping layer 626 becomes a partially deuterated layer, buthaving a deuterium concentration less than that of deuterated layer 624.In a specific embodiment, deuterated formation gases are employed toform a partially deuterated charge-trapping layer 626 having a deuteriumconcentration less than that of deuterated layer 624.

Referring to FIG. 6D, a top dielectric layer 628 is formed on the topsurface of multi-layer charge-trapping region 622. Top dielectric layer628 may be formed from any material, from any process, and have anythickness described in association with top dielectric layers 404C and504C from FIGS. 4 and 5, respectively. In accordance with an alternativeembodiment of the present invention, top dielectric layer 628 is formedby using deuterated formation gases. In such an embodiment, deuteratedtop dielectric layer 628 subsequently acts as a source of deuterium toform a trap-free layer in multi-layer charge-trapping region 622 duringa subsequent anneal process. In a specific alternative embodiment,deuterated top dielectric layer 628 is formed using formation gases suchas, but not limited to, SiD₄, SiD₂Cl₂ and N₂O.

Referring to FIG. 6E, a gate layer 630 is formed on the top surface oftop dielectric layer 628. Gate layer 630 may be formed from any materialand from any process described in association with gate layers 404D and504D from FIGS. 4 and 5, respectively. Thus, a gate stack 632 may beformed above substrate 602.

Referring to FIG. 6F, gate stack 632 is patterned to form a patternedgate stack 604 above substrate 602. Patterned gate stack 604 includes apatterned tunnel dielectric layer 604A, a patterned multi-layercharge-trapping region 604B, a patterned top dielectric layer 604C, anda patterned gate layer 604D. Patterned multi-layer charge trappingregion 604B includes a patterned deuterated layer 606 and a patternedcharge trapping layer 608. Gate stack 632 may be patterned to formpatterned gate stack 604 by any process suitable to providesubstantially vertical sidewalls for gate stack 604 with highselectivity to substrate 602. In accordance with an embodiment of thepresent invention, gate stack 632 is patterned to form patterned gatestack 604 by a lithography and etch process. In a specific embodiment,the etch process is an anisotropic etch process utilizing gases such as,but not limited to, carbon tetrafluoride (CF₄), O₂, hydrogen bromide(HBr) and chlorine (Cl₂).

Referring to FIG. 6G, it may be desirable to implant dopant impurityatoms 640 into the exposed portions of substrate 604 to form source anddrain tip extension regions 650. Source and drain tip extension regions650 will ultimately become part of source and drain regions subsequentlyformed, as described below. Thus, by forming source and drain tipextension regions 650 as defined by the location of patterned gate stack604, channel region 612 may be defined, as depicted in FIG. 6G. In oneembodiment, the conductivity type and the concentration of dopantimpurity atoms used to form source and drain tip extension regions 650are substantially the same as those used to form source and drainregions, described below.

Referring to FIG. 6H, it may be desirable to form a pair of dielectricspacers 614 on the sidewalls of patterned gate stack 604. Finally,referring to FIG. 6I, source and drain regions 610 are formed byimplanting dopant impurity atoms 660 into the exposed portions ofsubstrate 604. Source and drain regions 610 may have any characteristicsas those described in association with source and drain regions 410 and510 from FIGS. 4 and 5, respectively. In accordance with an embodimentof the present invention, the profile of source and drain regions 610 isdefined by dielectric spacers 614, patterned gate stack 604 and sourceand drain tip extension regions 650, as depicted in FIG. 61.

A nonvolatile charge trap memory device may be fabricated to include amulti-layer charge-trapping region having more than one deuteratedlayer. FIGS. 7A-C illustrate cross-sectional views representing steps inthe formation of a nonvolatile charge trap memory device, in accordancewith an embodiment of the present invention.

Referring to FIG. 7A, a tunnel dielectric layer 720 formed on the topsurface of a substrate 702 is provided. Substrate 702 may be composed ofany material and have any characteristics described in association withsubstrates 402 and 502 from FIGS. 4 and 5, respectively. Tunneldielectric layer 720 may be formed from any material, from any process,and have any thickness described in association with tunnel dielectriclayers 404A and 504A from FIGS. 4 and 5, respectively.

Referring to FIG. 7B, a multi-layer charge-trapping region 722 is formedon the top surface of tunnel dielectric layer 720. In accordance with anembodiment of the present invention, multi-layer charge-trapping region722 includes a first deuterated layer 724 between tunnel dielectriclayer 720 and a charge-trapping layer 726. Additionally multi-layercharge-trapping region 722 includes a second deuterated layer 727 on thetop surface of charge-trapping layer 726, as depicted in FIG. 7B. Firstdeuterated layer 724, charge-trapping layer 726, and second deuteratedlayer 727 may be composed of any materials and have any thicknessesdescribed in association with first deuterated layer 506,charge-trapping layer 508, and second deuterated layer 516,respectively, from FIG. 5. Multi-layer charge-trapping region 722 and,hence, first and second deuterated layers 724 and 727 andcharge-trapping layer 726 may be formed by any process suitable toprovide substantially uniform coverage above tunnel dielectric layer720. In accordance with an embodiment of the present invention,multi-layer charge-trapping region 722 is formed by a chemical vapordeposition process. In one embodiment, first deuterated layer 724 isformed first using deuterated formation gases, charge-trapping layer 726is formed next using non-deuterated formation gases and, finally, seconddeuterated layer 727 is formed using deuterated formation gases. In aspecific embodiment, multi-layer charge-trapping region 722 is composedsubstantially of silicon oxy-nitride, wherein first deuterated layer 724is formed first using formation gases such as, but not limited to, SiD₄,SiD₂Cl₂, N₂O, ND₃ and O₂. Charge-trapping layer 626 is then formed usingformation gases such as, but not limited to, non-deuterated-BTBAS, SiH₄,SiH₂Cl₂, N₂O, NH₃ and O₂. Finally, second deuterated layer 727 is formedusing formation gases such as, but not limited to, SiD₄, SiD₂Cl₂, N₂O,ND₃ and O₂. In a particular embodiment, first deuterated layer 724,charge-trapping layer 726 and second deuterated layer 727 are formed inthe same process step, i.e. in the same process chamber with a seamlesstransition from deuterated formation gases to non-deuterated formationgases and back to deuterated formation gases.

An abrupt deuterated and non-deuterated junction may be present at theinterfaces of first deuterated layer 724, second deuterated layer 727and charge-trapping layer 726. Thus, in accordance with an embodiment ofthe present invention, charge trapping layer 726 remains deuterium-free.Alternatively, some of the deuterium present in first and seconddeuterated layers 724 and 727 may migrate to charge-trapping layer 726during the deposition of charge-trapping layer 726 and second deuteratedlayer 727 or during subsequent high temperature process steps. That is,a gradient of deuterium atom concentration moving from highconcentration of deuterium in first and second deuterated layers 724 and727 ranging to low concentration of deuterium in charge-trapping layer726 may be formed. Thus, in accordance with an alternative embodiment ofthe present invention, charge-trapping layer 726 becomes a partiallydeuterated layer, but having a deuterium concentration less than that offirst and second deuterated layers 724. In a specific embodiment,deuterated formation gases are employed to form a partially deuteratedcharge-trapping layer 726 having a deuterium concentration less thanthat of deuterated layer 724.

Referring to FIG. 7C, process steps similar to those described inassociation with FIGS. 6D-I are carried out to form a nonvolatile chargetrap memory device having more than one deuterated layer. Thus, apatterned gate stack 704 is formed over a substrate 702. Source anddrain regions 710 are formed on either side of patterned gate stack 704,defining a channel region 712. Patterned gate stack 704 includes apatterned tunnel dielectric layer 704A, a patterned multi-layercharge-trapping region 704B, a patterned top dielectric layer 704C and apatterned gate layer 704D. Patterned multi-layer charge-trapping region704B includes a patterned first deuterated layer 706 and a patternedsecond deuterated layer 716 sandwiching patterned charge-trapping layer708.

Implementations and Alternatives

In one aspect the present disclosure is directed to charge trap memorydevices including one or more deuterated layers and a split multi-layercharge-trapping region with two or more nitride containing layers. FIG.8A is a block diagram illustrating a cross-sectional side view of onesuch embodiment.

Referring to FIG. 8A, the memory device 800 includes a gate stack 802with a split multi-layer charge-trapping region 804 formed over asurface 806 of a silicon substrate 808 or over a surface of a siliconlayer formed on a substrate. Generally, the device 800 further includesone or more diffusion regions 810, such as source and drain regions orstructures, aligned to the gate stack 802 and separated by a channelregion 812.

In addition to the multi-layer charge-trapping region 804, the gatestack 802 further includes a thin, tunnel dielectric layer 814 thatseparates or electrically isolates the gate stack from the channelregion 812, a top or blocking dielectric layer 816, and a gate layer818.

The multi-layer charge-trapping region 804 generally includes at leasttwo layers having differing compositions of silicon, oxygen andnitrogen. In one embodiment, the multi-layer charge-trapping regionincludes a first nitride layer 820 comprising a substantially trap-free,silicon-rich, oxygen-rich nitride, and a second nitride layer 822comprising a trap-dense, silicon-rich, nitrogen-rich, and oxygen-leannitride. It has been found that a silicon-rich, oxygen-rich, firstnitride layer 820 decreases the charge loss rate after programming andafter erase, which is manifested in a small voltage shift in theretention mode. A silicon-rich, nitrogen-rich, and oxygen-lean secondnitride layer 816 improves the speed and increases of the initialdifference between program and erase voltage without compromising acharge loss rate of memory devices made using an embodiment of thesilicon-oxide-oxynitride-oxide-silicon structure, thereby extending theoperating life of the device.

In addition to the first and second nitride layers 820, 822, themulti-layer charge-trapping region 804 further includes one or moredeuterated layers. In the embodiment shown the multi-layercharge-trapping region 804 includes a first deuterated layer 824separating the first nitride layer 820 from the tunnel dielectric layer814, and a second deuterated layer 826 separating the second nitridelayer 822 from the blocking dielectric layer 818. The first and seconddeuterated layers 824, 826, can be composed of a deuterated derivativeof the same material used to form the first and second nitride layers820, 822. For example, in an embodiment in which the first and secondnitride layers 820, 822 include silicon nitride and/or siliconoxynitride the first and second deuterated layers 824, 826, can becomposed of a deuterated derivative of silicon oxynitride.

In one embodiment, the total thickness of multi-layer charge-trappingregion 804 is in the range of 5-10 nanometers, the thicknesses of theindividual deuterated layers and nitride layers is approximately equal.

Multi-layer charge-trapping region 804 may have an abrupt interfacebetween the first deuterated layer 824 and the first nitride layer 820.That is, in accordance with one embodiment, the first nitride layer 820.Alternatively, a gradient of deuterium atom concentration moving fromhigh concentration of deuterium in the first deuterated layer 824ranging to low concentration of deuterium in the first nitride layer 820may be formed. Thus, in accordance with an alternative embodiment, thefirst nitride layer 820 is a partially deuterated layer, but having adeuterium concentration less than that of the first deuterated layer824.

Substrate 808 and, hence, channel region 812, may be composed of anymaterial suitable for semiconductor device fabrication. In oneembodiment, substrate 802 is a bulk substrate composed of a materialwhich may include, but is not limited to, silicon, germanium,silicon-germanium or a III-V compound semiconductor material. In anotherembodiment, substrate 808 includes a bulk layer with a top epitaxiallayer composed of a material which may include, but is not limited to,silicon, germanium, silicon-germanium, a III-V compound semiconductormaterial and quartz in and on which the memory device 800 is fabricated.Substrate 808 and, hence, channel region 812, may include dopantimpurity atoms. In a specific embodiment, the channel region 812includes polycrystalline silicon or polysilicon and is doped P-type, or,in an alternative embodiment, doped N-type. In another specificembodiment, the channel region 812 includes recrystallized polysiliconand is doped either P-type or N-type.

Source and drain regions 810 in substrate 808 may be any regions havingopposite conductivity to channel region 812. For example, in oneembodiment, the source and drain regions 810 are N-type doped regionswhile channel region 812 is a P-type doped region. In one version ofthis embodiment, the substrate 808 and, hence, channel region 812, iscomposed of boron-doped silicon having a boron concentration in therange of 1×10¹⁵-1×10¹⁹ atoms/cm³. Source and drain regions 810 arecomposed of phosphorous- or arsenic-doped regions having a concentrationof N-type dopants in the range of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specificembodiment, source and drain regions 810 have a depth in substrate 808in the range of 80-200 nanometers. In an alternative embodiment, sourceand drain regions 810 are P-type doped regions while channel region 812is an N-type doped region.

The tunnel dielectric layer 814 may be any material and have anythickness suitable to allow charge carriers to tunnel into themulti-layer charge-trapping region 804 under an applied gate bias whilemaintaining a suitable barrier to leakage when the memory device 800 isunbiased. In one embodiment, tunnel dielectric layer 814 is formed by athermal oxidation process and is composed of silicon dioxide or siliconoxy-nitride, or a combination thereof. In another embodiment, tunneldielectric layer 814 is formed by chemical vapor deposition or atomiclayer deposition and is composed of a dielectric layer which mayinclude, but is not limited to, silicon nitride, hafnium oxide,zirconium oxide, hafnium silicate, hafnium oxy-nitride, hafniumzirconium oxide and lanthanum oxide. In a specific embodiment, tunneldielectric layer 814 has a thickness in the range of 1-10 nanometers. Ina particular embodiment, tunnel dielectric layer 814 has a thickness ofapproximately 2 nanometers.

The blocking dielectric layer 816 may be any material and have anythickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of gate stack 802. In oneembodiment, the blocking dielectric layer 816 is formed by a chemicalvapor deposition process and is composed of silicon dioxide, siliconoxynitride, silicon nitride, or a combination thereof. In anotherembodiment, the blocking dielectric layer 816 is formed by atomic layerdeposition and is composed of a high-k dielectric layer which mayinclude, but is not limited to, hafnium oxide, zirconium oxide, hafniumsilicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanumoxide. In a specific embodiment, the blocking dielectric layer 816 has athickness in the range of 1-20 nanometers.

Gate layer 818 may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of aSONOS-type transistor, including doped polysilicon and ametal-containing material. In a specific embodiment, the gate layer 818has a thickness in the range of 1-20 nanometers.

In another embodiment shown in FIG. 8B the multi-layer charge-trappingregion 804 further includes an intermediate oxide or anti-tunnelinglayer 828 comprising an oxide separating the first nitride layer 820from the second nitride layer 822. During an erase of the memory device800 holes migrate toward the blocking dielectric layer 816, but themajority of trapped hole charges form in the second nitride layer 822.Electron charge accumulates at the boundaries of the second nitridelayer 822 after programming, and thus there is less accumulation ofcharge at the lower boundary of the first nitride layer 820.Furthermore, due to the anti-tunneling layer 828, the probability oftunneling by trapped electron charges in the second layer 822 issubstantially reduced. This may result in lower leakage current than forthe conventional memory devices.

Although shown and described above as having two nitride layers, i.e., afirst and a second layer, the present invention is not so limited, andthe multi-layer charge-trapping region may include a number, n, ofnitride layers, any or all of which may have differing stoichiometriccompositions of oxygen, nitrogen and/or silicon. In particular,multi-layer charge storing structures having up to five, and possiblymore, nitride layers each with differing stoichiometric compositions arecontemplated. At least some of these layers will be separated from theothers by one or more relatively thin oxide layers. However, as will beappreciated by those skilled in the art it is generally desirable toutilize as few layers as possible to accomplish a desired result,reducing the process steps necessary to produce the device, and therebyproviding a simpler and more robust manufacturing process. Moreover,utilizing as few layers as possible also results in higher yields as itis simpler to control the stoichiometric composition and dimensions ofthe fewer layers.

A method or forming or fabricating a memory device including a splitmulti-layer charge-trapping region according to one embodiment will nowbe described with reference to the flowchart of FIG. 9.

Referring to FIG. 9, the method begins with forming a tunnel dielectriclayer over a silicon containing layer on a surface of a substrate (900).As noted above, in one embodiment the tunnel dielectric layer comprisessilicon dioxide (SiO₂) and is formed or deposited a plasma oxidationprocess, In-Situ Steam Generation (ISSG) or a radical oxidation processin which hydrogen (H₂) and oxygen (O₂) gas are introduced into a processchamber to form radicals at a surface of the substrate to consume aportion of the substrate form the tunnel dielectric layer without anignition event to pyrolyze the H₂ and O₂.

The first deuterated layer is then formed on a surface of the tunnelingdielectric layer (902). The first deuterated layer can be formed ordeposited in a low pressure CVD process using a process gas comprising asilicon source, such as silane (SiH₄), chlorosilane (SiH₃Cl),dichlorosilane or DCS (SiH₂Cl₂), tetrachlorosilane (SiCl₄) orBis-TertiaryButylAmino Silane (BTBAS), an oxygen source, such as oxygen(O₂) or N₂O, and a nitrogen source containing deuterium, such asdeuterated-ammonia (ND₃).

Next, the first nitride or nitride containing layer of the multi-layercharge-trapping region is formed on a surface of the first deuteratedlayer (904). In one embodiment, the first nitride layer is formed ordeposited in a low pressure CVD process using a silicon source, such assilane (SiH₄), chlorosilane (SiH₃Cl), dichlorosilane or DCS (SiH₂Cl₂),tetrachlorosilane (SiCl₄) or Bis-TertiaryButylAmino Silane (BTBAS), anitrogen source, such as nitrogen (N₂), ammonia (NH₃), nitrogen trioxide(NO₃) or nitrous oxide (N₂O), and an oxygen-containing gas, such asoxygen (O₂) or N₂O. For example, the first nitride layer can bedeposited over the first deuterated layer by placing the substrate in adeposition chamber and introducing a process gas including N₂O, NH₃ andDCS, while maintaining the chamber at a pressure of from about 5milliTorr (mT) to about 500 mT, and maintaining the substrate at atemperature of from about 700 degrees Celsius to about 850 degreesCelsius and in certain embodiments at least about 760 degrees Celsius,for a period of from about 2.5 minutes to about 20 minutes. Inparticular, the process gas can include a first gas mixture of N₂O andNH₃ mixed in a ratio of from about 8:1 to about 1:8 and a second gasmixture of DCS and NH₃ mixed in a ratio of from about 1:7 to about 7:1,and can be introduced at a flow rate of from about 5 to about 200standard cubic centimeters per minute (sccm). It has been found that anoxynitride layer produced or deposited under these condition yields asilicon-rich, oxygen-rich, first nitride layer.

An anti-tunneling layer is then formed or deposited on a surface of thefirst nitride layer (906). As with the tunneling oxide layer, theanti-tunneling layer can be formed or deposited by any suitable means,including a plasma oxidation process, In-Situ Steam Generation (ISSG) ora radical oxidation process. In one embodiment, the radical oxidationprocess involves flowing hydrogen (H₂) and oxygen (O₂) gas into abatch-processing chamber or furnace to effect growth of theanti-tunneling layer by oxidation consumption of a portion of the firstnitride layer.

The second nitride layer of the multi-layer charge-trapping region isthen formed on a surface of the anti-tunneling layer (908). The secondnitride layer can be deposited over the anti-tunneling layer in a CVDprocess using a process gas including N₂O, NH₃ and DCS, at a chamberpressure of from about 5 mT to about 500 mT, and at a substratetemperature of from about 700 degrees Celsius to about 850 degreesCelsius and in certain embodiments at least about 760 degrees Celsius,for a period of from about 2.5 minutes to about 20 minutes. Inparticular, the process gas can include a first gas mixture of N₂O andNH₃ mixed in a ratio of from about 8:1 to about 1:8 and a second gasmixture of DCS and NH₃ mixed in a ratio of from about 1:7 to about 7:1,and can be introduced at a flow rate of from about 5 to about 20 sccm.It has been found that an oxynitride layer produced or deposited underthese condition yields a silicon-rich, nitrogen-rich, and oxygen-leansecond nitride layer.

In some embodiments, the second nitride layer can be deposited over theanti-tunneling layer in a CVD process using a process gas includingBTBAS and ammonia (NH₃) mixed at a ratio of from about 7:1 to about 1:7to further include a concentration of carbon selected to increase thenumber of traps therein. The selected concentration of carbon in thesecond oxynitride layer can include a carbon concentration of from about5% to about 15%.

Optionally, where the multi-layer charge-trapping region includes asecond deuterated layer the method of fabricating the memory device canfurther include forming the second deuterated layer on the secondnitride layer (910). As with the first deuterated layer, the seconddeuterated layer can be formed or deposited in a low pressure CVDprocess using a process gas comprising a silicon source, such as silane(SiH₄), chlorosilane (SiH₃Cl), dichlorosilane or DCS (SiH₂Cl₂),tetrachlorosilane (SiCl₄) or Bis-TertiaryButylAmino Silane (BTBAS), anoxygen source, such as oxygen (O₂) or N₂O, and a nitrogen sourcecontaining deuterium, such as deuterated-ammonia (ND₃).

Next, a top or blocking dielectric layer is formed on a surface of thesecond nitride layer of the multi-layer charge-trapping region or thesecond deuterated layer (912). As noted above the blocking dielectriclayer can include any suitable dielectric material including a high Kdielectric, silicon dioxide, silicon oxynitride, silicon nitride, or acombination thereof. In one embodiment, the blocking dielectric layerincludes a relatively thick layer of SiO₂ thermally grown or depositedusing a CVD process. Generally, the process involves exposing thesubstrate to a silicon source, such as silane, chlorosilane, ordichlorosilane, and an oxygen-containing gas, such as O₂ or N₂O in adeposition chamber at a pressure of from about 50 mT to about 1000 mT,for a period of from about 10 minutes to about 120 minutes whilemaintaining the substrate at a temperature of from about 650° C. toabout 850° C. Alternatively, as with the tunneling oxide layer theblocking dielectric layer can be formed or deposited by any suitablemeans, including a plasma oxidation process, In-Situ Steam Generation(ISSG) or a radical oxidation process.

Finally, a gate layer is formed on a surface of the blocking dielectriclayer (914). In one embodiment, the gate layer is formed by a CVDprocess and is composed of doped polysilicon. In another embodiment, thegate layer is formed by physical vapor deposition and is composed of ametal-containing material which may include, but is not limited to,metal nitrides, metal carbides, metal silicides, hafnium, zirconium,titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt andnickel.

In another aspect the present disclosure is also directed to multigateor multigate-surface memory devices including charge-trapping regionsoverlying two or more sides of a channel region formed on or above asurface of a substrate, and methods of fabricating the same. Multigatedevices include both planar and non-planar devices. A planar multigatedevice (not shown) generally includes a double-gate planar device inwhich a number of first layers are deposited to form a first gate belowa subsequently formed channel region, and a number of second layers aredeposited thereover to form a second gate. A non-planar multigate devicegenerally includes a horizontal or vertical channel region formed on orabove a surface of a substrate and surrounded on three or more sides bya gate.

FIG. 10A illustrates one embodiment of a non-planar multigate memorydevice including a charge-trapping region. Referring to FIG. 10A, thememory device 1000, commonly referred to as a finFET, includes a channelregion 1002 formed from a thin film or layer of semiconducting materialoverlying a surface 1004 on a substrate 1006 connecting a source 1008and a drain 1010 of the memory device. The channel region 1002 isenclosed on three sides by a fin which forms a gate 1012 of the device.The thickness of the gate 1012 (measured in the direction from source todrain) determines the effective channel length of the device.

In accordance with the present disclosure, the non-planar multigatememory device 1000 of FIG. 10A can include a split charge-trappingregion with one or more deuterated layers. FIG. 10B is a cross-sectionalview of a portion of the non-planar memory device of FIG. 10A includinga portion of the substrate 1006, channel region 1002 and the gate stack1012 illustrating a multi-layer charge-trapping region 1014. The gate1012 further includes a tunnel dielectric layer 1016 overlying theraised channel region 1002, a blocking dielectric 1018 and a gate layer1020 overlying the blocking layer to form a control gate of the memorydevice 1000. As with the embodiments described above In some embodimentsthe gate layer 1020 can include a metal or a doped polysilicon. Thechannel region 1002 and gate 1012 can be formed directly on substrate1006 or on an insulating or dielectric layer 1022, such as a buriedoxide layer, formed on or over the substrate.

Referring to FIG. 10B, in one embodiment the multi-layer charge-trappingregion 1014 includes at least a first deuterated layer 1024 overlyingthe tunnel dielectric layer 1016, a first nitride layer 1026 overlyingthe first deuterated layer 1024, and a second nitride layer 1028disposed on or above the first nitride layer. Generally, the secondnitride layer 1028 includes a silicon-rich, oxygen-lean nitride layerand includes a majority of a charge traps distributed in multiplecharge-trapping layers, while the first nitride layer 1026 includes anoxygen-rich nitride or silicon oxynitride, and is oxygen-rich relativeto the top charge-trapping layer to reduce the number of charge trapstherein. By oxygen-rich it is meant wherein a concentration of oxygen inthe first nitride layer 1026 is from about 15 to about 40%, whereas aconcentration of oxygen in top charge-trapping layer 1026 is less thanabout 5%.

In some embodiments, such as that shown, the multi-layer charge-trappingregion 1014 further includes at least one thin, intermediate oxide oranti-tunneling layer 1030 separating the second nitride layer 1028 fromthe first nitride layer 1026. As noted above, the anti-tunneling layer1030 substantially reduces the probability of electron charge thataccumulates at the boundaries of the second nitride layer 1028 duringprogramming from tunneling into the first nitride layer 1026.

As with the embodiments described above, either or both of the firstnitride layer 1026 and the second nitride layer 1028 can include siliconnitride or silicon oxynitride, and can be formed, for example, by a CVDprocess including N₂O/NH₃ and DCS/NH₃ gas mixtures in ratios and at flowrates tailored to provide a silicon-rich and oxygen-rich oxynitridelayer. The second nitride layer of the multi-layer charge-trappingregion is then formed on the middle oxide layer. The second nitridelayer 1028 has a stoichiometric composition of oxygen, nitrogen and/orsilicon different from that of the first nitride layer 1026, and mayalso be formed or deposited by a CVD process using a process gasincluding DCS/NH₃ and N₂O/NH₃ gas mixtures in ratios and at flow ratestailored to provide a silicon-rich, oxygen-lean second nitride layer1028.

In those embodiments including an anti-tunneling layer 1030 includingoxide, the anti-tunneling layer can be formed by oxidation of the firstnitride layer 1026, to a chosen depth using radical oxidation. Radicaloxidation may be performed, for example, at a temperature of 1000-1100degrees Celsius using a single wafer tool, or 800-900 degrees Celsiususing a batch reactor tool. A mixture of H₂ and O₂ gasses may beemployed at a pressure of 300-500 Torr for a batch process, or 10-15Torr using a single vapor tool, for a time of 1-2 minutes using a singlewafer tool, or 30 min-1 hour using a batch process.

In some embodiments, such as that shown, the multi-layer charge-trappingregion 1014 further includes a second deuterated layer 1032 overlyingthe second nitride layer 1028 and separating the second nitride layerfrom the blocking dielectric layer 1018. As with embodiments describedabove, the second deuterated layer 1032 has a concentration of deuteriumlower than a concentration of deuterium in the first deuterated layer1024.

In another embodiment, shown in FIGS. 11A and 11B, the memory device caninclude a nanowire channel formed from a thin film of semiconductingmaterial overlying a surface on a substrate connecting a source and adrain of the memory device. By nanowire channel it is meant a conductingchannel region formed in a thin strip of crystalline silicon material,having a maximum cross-sectional dimension of about 10 nanometers (nm)or less, and more preferably less than about 6 nm. Optionally, thechannel region can be formed to have <100> surface crystallineorientation relative to a long axis of the channel region.

Referring to FIG. 11A, the memory device 1100 includes a horizontalnanowire channel region 1102 formed from a thin film or layer ofsemiconducting material on or overlying a surface on a substrate 1106,and connecting a source 1108 and a drain 1110 of the memory device. Inthe embodiment shown, the device has a gate-all-around (GAA) structurein which the nanowire channel region 1102 is enclosed on all sides by agate 1112 of the device. The thickness of the gate 1112 (measured in thedirection from source to drain) determines the effective channel regionlength of the device.

In accordance with the present disclosure, the non-planar multigatememory device 1100 of FIG. 11A can include a split multi-layercharge-trapping region. FIG. 11B is a cross-sectional view of a portionof the non-planar memory device of FIG. 11A including a portion of thesubstrate 1106, nanowire channel region 1102 and the gate 1112illustrating a split multi-layer charge-trapping region. Referring toFIG. 11B, the gate 1112 includes, in addition to a split multi-layercharge-trapping region, a tunnel dielectric layer 1114 overlying thenanowire channel region 1102, a blocking dielectric 1116 and a gatelayer 1118 overlying the blocking layer to form a control gate of thememory device 1100. The gate layer 1118 can comprise a metal or a dopedpolysilicon.

The split multi-layer charge-trapping region includes at least a firstdeuterated layer 1120 overlying the tunnel dielectric layer 1114, aninner or first nitride layer 1122 or layer comprising nitride overlyingthe first deuterated layer 1120, and an outer or second nitride layer1124 or layer comprising nitride overlying the first nitride layer 1122.Generally, the second nitride layer 1124 comprises a silicon-rich,oxygen-lean nitride layer and comprises a majority of a charge trapsdistributed in split multi-layer charge-trapping region, while the firstnitride layer 1122 comprises an oxygen-rich nitride or siliconoxynitride, and is oxygen-rich relative to the second nitride layer 1124to reduce the number of charge traps therein.

In some embodiments, such as that shown, the multi-layer charge-trappingregion further includes at least one thin, intermediate oxide oranti-tunneling layer 1126 separating the second nitride layer 1124 fromthe first nitride layer 1122. As noted above, the anti-tunneling layer1126 substantially reduces the probability of electron charge thataccumulates at the boundaries of the second nitride layer 1124 duringprogramming from tunneling into the first nitride layer 1122.

As with the embodiment described above, either or both of the firstnitride layer 1122 and the second nitride layer 1124 can comprisesilicon nitride or silicon oxynitride. The first nitride layer 1122 canbe formed, for example, by a CVD process including N₂O/NH₃ and DCS/NH₃gas mixtures in ratios and at flow rates tailored to provide asilicon-rich and oxygen-rich first nitride layer. The second nitridelayer 1124 has a stoichiometric composition of oxygen, nitrogen and/orsilicon different from that of the first nitride layer 1122, and mayalso be formed or deposited by a CVD process using a process gasincluding DCS/NH₃ and N₂O/NH₃ gas mixtures in ratios and at flow ratestailored to provide a silicon-rich, oxygen-lean second nitride layer.

In those embodiments including an anti-tunneling layer 1126 comprisingoxide, the anti-tunneling layer can be formed by oxidation of the firstnitride layer 1122, to a chosen depth using radical oxidation. Radicaloxidation may be performed, for example, at a temperature of 1000-1100degrees Celsius using a single wafer tool, or 800-900 degrees Celsiususing a batch reactor tool. A mixture of H₂ and O₂ gasses may beemployed at a pressure of 300-500 Torr for a batch process, or 10-15Torr using a single vapor tool, for a time of 1-2 minutes using a singlewafer tool, or 30 min-1 hour using a batch process.

In some embodiments, such as that shown, the multi-layer charge-trappingregion 1014 further includes a second deuterated layer 1128 overlyingthe second nitride layer 1124 and separating the second nitride layerfrom the blocking dielectric layer 1116. As with embodiments describedabove, the second deuterated layer 1128 has a concentration of deuteriumlower than a concentration of deuterium in the first deuterated layer1120.

FIG. 11C illustrates a cross-sectional view of a vertical string ofnon-planar multigate devices 1100 of FIG. 11A arranged in a Bit-CostScalable or BiCS architecture 1130. The architecture 1130 consists of avertical string or stack of non-planar multigate devices 1100, whereeach device or cell includes a channel region 1102 overlying thesubstrate 1106, and connecting a source and a drain (not shown in thisfigure) of the memory device, and having a gate-all-around (GAA)structure in which the nanowire channel region 1102 is enclosed on allsides by a gate 1112. The BiCS architecture reduces number of criticallithography steps compared to a simple stacking of layers, leading to areduced cost per memory bit.

In another embodiment, the memory device is or includes a non-planardevice comprising a vertical nanowire channel formed in or from asemiconducting material projecting above or from a number of conducting,semiconducting layers on a substrate. In one version of this embodiment,shown in cut-away in FIG. 12A, the memory device 1200 comprises avertical nanowire channel region 1202 formed in a cylinder ofsemiconducting material connecting a source 1204 and drain 1206 of thedevice. The channel region 1202 is surrounded by a tunnel dielectriclayer 1208, a multi-layer charge-trapping region 1210, a blocking layer1212 and a gate layer 1214 overlying the blocking layer to form acontrol gate of the memory device 1200. The channel region 1202 caninclude an annular region in an outer layer of a substantially solidcylinder of semiconducting material, or can include an annular layerformed over a cylinder of dielectric filler material. As with thehorizontal nanowires described above, the channel region 1202 cancomprise polysilicon or recrystallized polysilicon to form amonocrystalline channel. Optionally, where the channel region 1202includes a crystalline silicon, the channel can be formed to have <100>surface crystalline orientation relative to a long axis of the channel.

In some embodiments, such as that shown in FIG. 12B, the multi-layercharge-trapping region 1210 can be a split multi-layer charge-trappingregion including at least a first deuterated layer 1216 overlying thetunnel dielectric layer 1208, an inner or first nitride layer 1218 orlayer comprising nitride overlying the first deuterated layer 1216, andan outer or second nitride layer 1220 or layer comprising nitrideoverlying the first nitride layer 1218. Optionally, as in the embodimentshown the first and second nitride layers 1218, 1220, can be separatedby an intermediate oxide or anti-tunneling layer 1222.

As with the embodiments described above, either or both of the firstnitride layer 1218 and the second nitride layer 1220 can comprisesilicon nitride or silicon oxynitride. The first nitride layer 1218 canbe formed, for example, by a CVD process including N₂O/NH₃ and DCS/NH₃gas mixtures in ratios and at flow rates tailored to provide asilicon-rich and oxygen-rich first nitride layer. The second nitridelayer 1220 has a stoichiometric composition of oxygen, nitrogen and/orsilicon different from that of the first nitride layer 1218, and mayalso be formed or deposited by a CVD process using a process gasincluding DCS/NH₃ and N₂O/NH₃ gas mixtures in ratios and at flow ratestailored to provide a silicon-rich, oxygen-lean second nitride layer.

In some embodiments, such as that shown, the multi-layer charge-trappingregion 1210 further includes a second deuterated layer 1224 overlyingthe second nitride layer 1220 and separating the second nitride layerfrom the blocking dielectric layer 1212. As with embodiments describedabove, the second deuterated layer 1224 has a concentration of deuteriumlower than a concentration of deuterium in the first deuterated layer1216.

Thus, a nonvolatile charge trap memory device has been disclosed. Thedevice includes a substrate having a channel region and a pair of sourceand drain regions. A gate stack is above the substrate over the channelregion and between the pair of source and drain regions. In accordancewith an embodiment of the present invention, the gate stack includes amulti-layer charge-trapping region having a first deuterated layer. Inone embodiment, the multi-layer charge-trapping region further includesa deuterium-free charge-trapping layer. In an alternative embodiment,the multi-layer charge-trapping region includes a partially deuteratedcharge-trapping layer having a deuterium concentration less than that ofthe first deuterated layer.

1. A charge trap memory device, comprising: a substrate having a sourceregion, a drain region, and a channel region formed from a thin film ofsemiconducting material overlying a surface on the substrate andelectrically connecting the source region and drain region; a tunneldielectric layer disposed above the substrate over the channel region;and a multi-layer charge-trapping region including a first deuteratedlayer disposed on the tunnel dielectric layer, a first nitride layerdisposed on the first deuterated layer and a second nitride layerdisposed above the first nitride layer, wherein the first nitride layercomprises a substantially trap-free, oxygen-rich nitride layer, and thesecond nitride layer comprises a trap-dense, oxygen-lean nitride layer.2. The memory device of claim 1, wherein the first deuterated layercomprises a deuterated derivative of a material used to form the firstnitride layer.
 3. The memory device of claim 2, wherein the firstnitride layer is deuterated, and wherein a concentration of deuterium inthe first nitride layer is less than a concentration of deuterium in thefirst deuterated layer.
 4. The memory device of claim 3, wherein thereis a gradient of deuterium atom concentration from a high concentrationof deuterium in the first deuterated layer to a low concentration ofdeuterium in the first nitride layer.
 5. (canceled)
 6. The memory deviceof claim 1, further comprising a second deuterated layer disposed abovethe second nitride layer.
 7. The memory device of claim 1, wherein thechannel region comprises recrystallized polysilicon.
 8. The memorydevice of claim 1, wherein the multi-layer charge-trapping regionfurther comprises an anti-tunneling layer comprising an oxide separatingthe first nitride layer from the second nitride layer.
 9. A charge trapmemory device, comprising: a substrate having a source region, a drainregion, and a channel region formed from a thin film of semiconductingmaterial overlying a surface on the substrate and electricallyconnecting the source and drain; a tunnel dielectric layer disposedabove the substrate over the channel region; and a multi-layercharge-trapping region including a first deuterated layer disposed onthe tunnel dielectric layer, a first nitride layer disposed on the firstdeuterated layer and a second nitride layer disposed above the firstlayer.
 10. The memory device of claim 9, wherein the first nitride layeris deuterated, and wherein a concentration of deuterium in the firstnitride layer is less than a concentration of deuterium in the firstdeuterated layer.
 11. The memory device of claim 9, further comprising asecond deuterated layer disposed above the second nitride layer.
 12. Thememory device of claim 9, wherein the channel region comprisespolysilicon.
 13. The memory device of claim 12, wherein the channelregion comprises recrystallized polysilicon. 14.-20. (canceled)